1. Field of the Invention
The present invention relates to a surface profile measurement apparatus, and in particular to a surface profile measurement apparatus for measuring the profile of a surface of an object having a curvature.
2. Description of the Related Art
Conventionally, a profile of a surface of an object, including roughness, irregularities, and shape, has been measured using various optical apparatuses. In a typical example of such measurement, a reference plane is provided with respect to the surface of the object, and an interference fringe caused by light reflected by the surface and by the reference plane is studied to measure the surface profile of the object.
For example, the shape of a diamond indenter for use in measurement of the hardness of mechanical parts and so on may be measured. In a Rockwell hardness testing apparatus, a diamond indenter is pressed onto the surface of an object so that the hardness of the object is measured based on the depth of a concave resulted on its surface. The diamond indenter to be pressed onto the object has a cone shape with a vertex of 120xc2x0 having a spherical tip end of a curvature radius 0.2 mm. In hardness measurement, measure of precision of the vertex angle and curvature radius of the cone must be precisely estimated before actual hardness measurement as these values severely affect the measurement result.
A known apparatus for measuring the vertex angle of a cone is a microscopic interferometer (Bulletin of NRLM Vol. 18, No. 4, p. 87). This apparatus measures a vertex angle of a cone based on an interference fringe caused by a reference plane and a generatrix portion of the cone.
The curvature radius of a spherical tip end can be measured using an interferometer. Alternatively, it can be measured using a micro-collimation method, disclosed in Bulletin of NRLM (Vol. 18, No. 4, p. 79). A micro-collimation method utilizes the fact the maximum light intensity is observed when the light is focused onto the tip end of a spherical surface and the curvature center of the tip.
The above described measurement of a diamond indenter, however, requires different apparatuses for measurements of a curvature radius of a cone and of the vertex angle of the same. As a result, an object diamond indenter must be mounted to a different apparatus for every measurement and a setting error must be evaluated for every measurement. This leads to a problem that a relatively long time is required to complete procedures such as the setting of an object and measurement.
The present invention has been conceived to overcome the above problems and aims to provide a surface profile measurement apparatus for efficiently measuring the surface profile of an object.
Another object of the present invention is to provide a surface profile measurement apparatus suitable for use in measurement of the surface profile of an indenter for use in hardness measurement.
In order to achieve the above objects, according to the present invention, there is provided a surface profile measurement apparatus for measuring surface profile of an object having a surface with a curvature and mounted movably, comprising an interference optical system for forming an interference fringe created by light from a light source reflected by the object and light from the light source reflected by a reference body; a surface profile measurement section for measuring the surface profile of the object based on the interference fringe; a condenser optical system for condensing the light reflected by the object; and a curvature radius measurement section for measuring a curvature radius of the object based on variation of the light condensed by the condenser optical system, while translationally moving the object.
The above structure enables measurement of a surface profile of an object and measurement of a curvature radius of a portion of an object having a curvature, using the surface profile measurement apparatus of the present invention.
It should be noted that xe2x80x9ca surface with a curvaturesxe2x80x9d as used here refers to a portion of a surface of an object, which could roughly be consider as a section of a sphere. It should be further noted that xe2x80x9csurface profilexe2x80x9d refers here to information concerning the characteristics, such as roughness, irregularity, and shape.
A path along which the light irradiates the object in the condenser optical system and a path along which the light irradiates the object in the interference optical system may preferably coincide. This structure enables reduction of an error caused in setting an object, for example, and the number of parts constituting the optical system.
Preferably, the reference body may include a plurality of reference body pieces which are mutually switchable by means of reference body switching means. This structure enables highly accurate measurement as it allows switching of reference bodies according to the surface profile of an object to be measured.
The apparatus may further preferably comprise measurement switching means for switching measurement of the curvature radius of the object and measurement of the surface profile of the object. This structure enables curvature radius measurement and surface profile measurement independently.
Still further, the object may be mounted allowing rotation around an axis thereof.
Yet further, the object may be mounted allowing rotation around an axis vertical to an optical axis of the light irradiating the object. Because such a structure allows an object to be rotated, a larger portion of the surface of the object can be measured.
Preferably, the object may have a conical shape, and the surface profile measurement section may measure a vertex angle of the cone-shaped object based on variation of the interference fringe caused as the object rotates. This structure enables measurement of the vertex angle of a cone.
According to another aspect of the present invention, there is provided a surface profile measurement apparatus for measuring surface profile of an object having a partially spherical tip end and a cone-shaped substrate and mounted movably, comprising an interference optical system for forming an interference fringe created by light from a light source reflected by the object and light from the light source reflected by a reference body; a surface profile measurement section for measuring the surface profile of the object based on the interference fringe; a condenser optical system for condensing the light reflected by the object; and a curvature radius measurement section for measuring a curvature radius of the object based on variation of the light condensed by the condenser optical system, while moving translationally moving the object, wherein the surface profile measurement section measures a vertex angle of the cone-shaped object based on variation of the interference fringe created as the object rotates around an axis vertical to an optical axis of light irradiating the object.
This structure enables measurement of the curvature radius of the tip end and the vertex angle of the cone portion of an object having a partially spherical tip end and a cone-shaped substrate.
According to still another aspect of the present invention, there is provided a surface profile measurement apparatus for measuring surface profile of an object having a partially spherical tip end and a cone-shaped substrate and mounted movably, comprising an interference optical system for forming an interference fringe created by light from a light source reflected by the object and light from the light source reflected by a reference body and a surface profile measurement section for measuring the surface profile of the object based on the interference fringe, wherein the reference body includes a reference surface and a reference sphere, which are mutually switchable by means of reference body switching means, and the surface profile measurement section measures an angle of a vertex of the cone-shaped object based on variation of an interference fringe created by the reference surface and the surface of the object, and measures surface profile of the partially spherical tip end of the object based on variation of an interference fringe created by the reference sphere and the object, both interference fringes being formed as the object rotates around an axis vertical to an optical axis of the light irradiating the object.
This structure enables measurement of the curvature radius of the tip end of an object having a partially spherical tip end and a cone-shaped substrate, and measurement of the vertex angle of the cone portion of the object.
The apparatus may further preferably comprise a condenser optical system for condensing light reflected by the object and a curvature radius measurement section for measuring a curvature radius of the object based on variation of the light condensed by the condenser optical system, while translationally moving the object.